T
Tom Tarlton
Guest
"Engine gurus: I have a pair
"Engine gurus: I have a pair of Mercruiser 8.1 S Horizon engines (model number 3-S4871JN1)in a Bertram 33. A few months back, the port side exhaust manifold on the starboard engine began leaking where the hose fitting connects to bottom center of the manifold. The engines have closed cooling systems with heat exchanger. Original manifolds are cast aluminum; Mercruiser has since gone to a cast iron unit for replacement. I notice a tremendous difference in surface temperature between the aluminum and cast iron units on their lower sides near their connection to the block. For instance, at 700 rpm, the cast iron manifold averages about 250 degrees, the aluminum unit 185 degrees. At 900 rpm, 315 degrees vs 215, at 1800 rpm, 480 degrees vs 270 degrees, and at 2700 rpm, the cast iron manifold reaches 590 degrees while the aluminum unit averages about 330 degrees. During the initial runs after the cast iron manifold was installed, I noticed some smoke coming off it which led me to investigate. My mechanic though it was probably excess paint/grease, etc burning off, and the smoke disappeard after the fourth run. The upper area of the cast iron manifold is quite cool, about 10 degrees warmer than the aluminum unit, sufficiently cool to keep the engine guardian system happy, as overheat alarms are not being triggered by the thermostat in the top of the manifold. The engine room is a bit warmer, but I can't imagine how hot it would be if all four of the exhaust manifolds were cast iron. Any thoughts on this?
Thanks"
"Engine gurus: I have a pair of Mercruiser 8.1 S Horizon engines (model number 3-S4871JN1)in a Bertram 33. A few months back, the port side exhaust manifold on the starboard engine began leaking where the hose fitting connects to bottom center of the manifold. The engines have closed cooling systems with heat exchanger. Original manifolds are cast aluminum; Mercruiser has since gone to a cast iron unit for replacement. I notice a tremendous difference in surface temperature between the aluminum and cast iron units on their lower sides near their connection to the block. For instance, at 700 rpm, the cast iron manifold averages about 250 degrees, the aluminum unit 185 degrees. At 900 rpm, 315 degrees vs 215, at 1800 rpm, 480 degrees vs 270 degrees, and at 2700 rpm, the cast iron manifold reaches 590 degrees while the aluminum unit averages about 330 degrees. During the initial runs after the cast iron manifold was installed, I noticed some smoke coming off it which led me to investigate. My mechanic though it was probably excess paint/grease, etc burning off, and the smoke disappeard after the fourth run. The upper area of the cast iron manifold is quite cool, about 10 degrees warmer than the aluminum unit, sufficiently cool to keep the engine guardian system happy, as overheat alarms are not being triggered by the thermostat in the top of the manifold. The engine room is a bit warmer, but I can't imagine how hot it would be if all four of the exhaust manifolds were cast iron. Any thoughts on this?
Thanks"